This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Prions are infectious protein aggregates which cause neurodegeneration and death in mammals. Cultured neuronal cells have been used in the study of prions. The study of prion propagation in these cell lines is complicated by an inability to differentiate prions supplied to initiate the infection from new cellular prions. Introducing an novel epitope into cellular prion protein has been used previously to identify prion origin. This technique is problematic because pertubations to protein structure may influence prion transmission. Labeled amino acids in the culture medium would be incorporated into newly synthesized prions. The isotopic label in combination with mass spectroscopy would allow us to identify prions produced in the cell culture. Collaboration with the UCSF Mass Spectrometry Facility would give us access to the instrumentation necessary to measure the extent of isotopic incorporation into the prions we have generated. We have had successful collaborations on similar projects. We envision that this project would use the protocols we have established previously.